1. Field of the Invention
Our invention deals with hydraulic torque converters and is directed more specifically to the improved design of a closed toroidal circuit of a converter through which the working fluid is recirculated for hydrodynamic power transmission. The improved circuit design according to our invention permits a variety of arrangements of impeller, turbine and reactor members or elements affording a variety of constructional and operational characteristics.
2. Description of the Prior Art
Hydraulic torque converters of various designs have been suggested and employed for various applications. U.S. Pat. No. 3,125,857 to Schneider, for example, proposes a torque converter which permits the impeller, turbine and reactor members to be separately cast in one piece. The blades of all the converter members are curved, but not twisted, between their inlet and outlet tips. Therefore, in the making of sand cores preparatory to separately casting the converter members, the master blades therefor can be easily removed from the hardened cores. Although the master blades for the impeller and turbine blades can be removed altogether in the axial direction, however, the stator master blades must be removed individually in the radially inward direction.
The converter which has been actually manufactured according to this Schneider patent has a stall torque ratio of approximately 3.3 at a maximum. It permits the mounting of a free-wheel or overrunning clutch in a position radially inwardly of the toroidal circuit, for convenient use as a compact, two-phase machine.
U.S. Pat. No. 3,360,935, also to Schneider, proposes a torque converter designed to absorb increased horsepower. The impeller, turbine and reactor members of this converter are also easy to manufacture since their blades are not twisted. Depending on blade design, moreover, the converter members can be formed by casting with the use of integral cores, as in the first mentioned Schneider patent. The stall torque ratio of the converter according to this second mentioned Schneider patent can be made as high as five or more, and its speed ratio (output speed/input speed) can be made more than two. An additional feature resides in the fact that at a constant input speed, the input or primary torque does not vary so much with changes in speed ratio.
U.S. Pat. No. 3,071,928 to Dundore et al. discloses a torque converter designed to afford the application of maximum torque over a widely varying torque range. The impeller and turbine members of this converter are formed by casting, and its reactor member by sheet-metal working on drawn pieces. The manufacturing costs of the converter are therefore comparatively low. Some converter models manufactured in accordance with this Dundore et al. patent have a maximum stall torque ratio of slightly more than three.
The number of turbine blades according to the Dundore et al. patent is comparatively small, being specified as ranging from 24 to 30. The radial length of the turbine blades must therefore be made considerably great for proper absorption of the momentum of the working fluid by the turbine. This necessitates reduction in the minimum or inner radius of the toroidal circuit of the converter. Thus, the width of the circuit must also be reduced as will become apparent from the following considerations.
In the toroidal circuit of the converter proposed by Dundore et al., the diameter D of a circle inscribed between the outer and inner walls of the circuit and located in the radially outermost position thereof is defined by the formula: ##EQU1## wherein R is the maximum or outer radius of the circuit, and r is the distance of the center of the circle from the axis of the converter. Contrastingly, according to the first mentioned Schneider patent (U.S. Pat. No. 3,125,857): ##EQU2##
A comparison of the above two formulas will show that the width of the circuit according to the Dundore et al. patent is about 20 to 40 percent less than that according to the Schneider patent. The amount of the fluid recirculating in the former circuit is therefore considerably less than that of the fluid in the latter circuit. In other words, for a given maximum radius of the circuit, the Dundore et al. converter is capable of transmitting less power. Stated conversely, the converter must be of greater size for transmitting a given power.
As mentioned, the turbine blades of the Dundore et al. converter need to be of increased radial length because of their comparatively small number. The minimum radius of its circuit is 0.268 R. This is far less than the minimum radius of the circuit according to the first mentioned Schneider patent, which radius is approximately 0.351 R. It is therefore practically impossible to mount an overrunning clutch radially inwardly of the circuit in the Dundore et al. converter.
A further torque converter suggested by U.S. Pat. No. 3,105,396, also to Dundore et al., is of the dual reactor type. Essentially, it is identical with the first mentioned Dundore et al. converter except that the second reactor element is disposed radially inwardly of the impeller member. The first and second reactor elements can both be equipped with overrunning clutches for three-phase operation. As explained in connection with the first mentioned Dundore et al. patent, however, the minimum radius of the circuit is so small that the clutches cannot possibly be disposed radially inwardly thereof. Other characteristics are also identical with those of the first mentioned Dundore et al. converter.
Japanese Patent Publication No. 38-10468 also discloses a torque converter of the dual reactor type. In the arrangement of its members the converter according to this Japanese patent is identical with the converter according to the second mentioned Schneider U.S. Pat. No. 3,360,935 except that the former has an additional reactor disposed in the outer, axial flow portion of the circuit. Its characteristics are also similar to those of the second mentioned Schneider et al. converter.
An additional prior art converter construction, in very widespread use, is one in which the outer and inner walls of the toroidal circuit are substantially circular in shape and which has a split reactor. This split reactor is capable of functioning either as an integral member or as separate elements, with overrunning clutches mounted radially inwardly of the circuit. Although of great utility as a compact, polyphase machine, the converter has twisted blades, which of course are difficult of manufacture.
The above enumerated prior art torque converters are considered typical of those in current use. In view of their constructional and operational characteristics, these converters may be put to selective use to suit the particular applications intended. A problem arise, however, that the toroidal circuits of the listed converters are all more or less different in shape. No standardized parts or components can be employed for the different converters. They must be designed and manufactured separately, at significantly increased costs.